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what is the scanning and tunneling electron microscope used for

what is the scanning and tunneling electron microscope used for

scanning tunneling microscope (STM)

A scanning tunneling microscope (STM) is a device that obtains images of the atoms on the surfaces of materials. The STM is not an optical microscope; instead, it works by detecting electrical forces with a probe that tapers down to a point only a single atom across.

The probe in the STM sweeps across the surface of which an image is to be obtained. The electron shells, or clouds, surrounding the atoms on the surface produce irregularities that are detected by the probe and mapped by a computer into an image. The resolution of the image is on the order of one nanometer (1 nm) or less, where 1 nm = 0.000000001 meter = 10-9 m.

The STM has applications in molecular science, also known as nanotechnology. It can be used to move atoms individually, as well as to generate high-resolution maps of material surfaces.

How Scanning tunneling Microscope works ?

Scanning tunneling microscope scans the electrons at fixed distance. First, a voltage bias is applied and the conducting tip is placed closer to the sample to be examined.The tip is also known as stylus ,stylus is extremely sharp and usually made up of a finest diamond , which is switched off when the tip and sample are sufficiently close.

When a conducting edge or tip is brought near the surface to be tested, a specific voltage variation is applied which allows electrons to pass through the tunnel in the vacuum. In the result, tunneling current is obtained which is the function of accurate tip position. Information is gathered by monitoring the current according to the tip position which scans across the surface, and this information is usually displayed in form of image.

The stylus is moved in the upward direction and then lowered in order to keep the each signal undistorted .This allows it to follow even the smallest data of the surface it is scanning. Storing the vertical movement of the stylus makes it possible to observe the structure of the surface atomically in organized manner. A profile of the scanned surface is created, and with the help of this profile contouring map is generated from the computer system attached to the microscope. The STM works best with conductors. But it can also work with the organic molecules all required is to fix organic molecules on a surface and study their structures. This technique has been used in the study of DNA molecules.

 

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